Radionuclide Regurgitant Index: Value and Limitations WILFRED LAM, MD, FACC DAN PAVEL, MD ERNEST BYROM, PhD AMJAD SHEIKH, MD DAVID BEST, MD KENNETH ROSEN, MD, FACC Chicago, Illinois From the Section of Cardiology, Department of Medicine, and the Section of Nuclear Medicine, Department of Radiology, Abraham Lincoln School of Medicine, Unlversity of Illinois College of Medicine, Chicago, Ilnnois. This study was supported in part by Institutional Training Grant HL 07387 from the National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland. Manuscript received June 16, 1980; revised manuscript received September 23, 1980, accepted September 26, 1980. Address for reprints: Wilfred Lam, MD, Uni- versity of Illinois Hospiil, Cardiology Section, P.O. Box 6998, Chicago, Illinois 60680. The radionuclide regurgitant index, defined as left ventricular/right ven- tricular stroke counts obtained from gated equilibrium studies, has been reported to predict the presence and severity of left-sided valve regur- gitation. This study evaluated the radionuclide regurgitant index in 100 patients in whom left-sided valve regurgitation was angiographically graded (0 to 4+) with regard to most severe mitral or aortic regurgitation. Regurgitation was graded 0 in 44 of the 100 patients, l+ in 22, 2-I in 8, 3-F in 8 and 4+ in 20. The radionuclide regurgitant index was 0.9 to 1.5 in 51 patients, 1.8 to 2.4 in 23 and 2.5 to 12.0 in 28. The mean radionuclide regurgitant index was 1.34 in the group with no regurgitation and 1.80 in those with l+, 2.01 in those with 2-i-, 2.80 in those with 3-F and 3.85 in those with 4-F regur- gitation. There was a significant difference (p <0.05) in the radionuclide regurgitant index between patients with no regurgitation and each group with regurgitation and between groups with regurgitation separated by two or more grades of angiographic regurgitation. Twelve patients had a discordant radionuclide regurgitant index; their index either predicted clinically significant or severe regurgitation when they had no or trivial regurgitation, or predicted no or trivial regurgitation when they had clinically significant regurgitation. Eight of 10 patients with a left ventricular ejection fraction of less than 0.30 had a discordant index (p <O.OOOS). All three patients with mitral valve prolapse associated with frequent ventricular extrasystoles had a discordant index (p <O.OOOS). Recently, gated radionuclide equilibrium studies have been utilized as a noninvasive technique for measuring the severity of valve regurgitation. Rigo et a1.l reported a radionuclide index of left-sided valve regurgitation derived from gated cardiac blood pool studies. This index was defined as the ratio of left to right ventricular stroke counts, calculated from the difference in counts in each ventricle between end-diastole and end- systole. On the basis of studies iti 40 patients (31 with cardiac catheter- ization), they suggested that this index was useful in assessing the presence and severity of aortic or mitral regurgitation, or both. In this study, we measured the radionuclide regurgitant index in 100 patients undergoing both cardiac catheterization and electrocardi- ographically synchronized radionuclide cardiac studies in an attempt to assess further the utility of this new noninvasive measure of left-sided valve regurgitation. In addition, we attempted to define subgroups of patients whose radionuclide regurgitant index appeared to predict spuriously the presence or absence of significant regurgitation. Methods Patient selection: The study group consisted of 100 consecutive patients undergoing clinically indicated diagnostic cardiac catheterization and radio- nuclide cardiac equilibrium studies. The catheterization and radionuclide studies were performed within a period of 2 weeks in all patients and within 3 days in 66 patients. There was no change in the clinical or hemodynamic status of any patient between the two studies. Patients were excluded from consideration and 292 February 1981 The American Journal of CARDIOLOGY Volume 47